A piston pump is a high pressure pump of the positive displacement variety which substantially consists of a powerful electric motor, transmission mechanism and crank mechanism, as well as a pump assembly with a pump block, valves and a number of plungers or pistons. The rotary movement from the electric motor is converted by means of the transmission mechanism into the reciprocating movement of the pistons.
One common field of practical application for a high pressure pump of the piston type is in a homogenizer. In those cases where the high pressure pump is employed as a homogenizer, the pump block is supplemented with one or more homogenization apparatuses or counter-pressure apparatuses in which the homogenization process takes place.
Homogenization is an often-employed industrial process, above all within the dairy industry, where homogenization is employed for splitting the fat globules in milk and thereby preventing cream setting. Almost all consumer milk is homogenized today. This employment within the food industry entails that extremely stringent demands on hygiene are placed on not only the homogenizers but also all ancillary equipment.
The movement of the piston pump implies that, on the suction side of the pump, a liquid column of product such as milk is to be accelerated on each stroke of the piston. This entails that the product flow will be greatly pulsating and, in order to avoid the risk that this damages the pump and ancillary equipment, it is necessary to provide the piston pump with dampers.
In its simplest form, a damper consists of a partly air-filled upright tube in direct connection to the piston pump. Many homogenizers available on the market feature as standard such dampers on both the suction side and the pressure side of the pump.
In most practical applications, the above-described type of damper is efficient from the point of view of damping, but cannot normally be cleaned in the CIP system of the dairy plant (Cleaning In Place). The upright tube section must be dismounted and washed manually. Nor is such a damper suitable for aseptic applications, since the upright tube is difficult to sterilize in connection with the sterilization of the remaining equipment.
Gradually as such a damper is in operation, the air entrapped in the upright tube will, in due course, be “consumed” by the product flow. It has hitherto not been possible to replenish air while the plant is in operation, but it has instead been necessary to stop production, which has entailed both time losses and losses of product.
Requirements on higher output capacities and longer running times, for example within the food industry, as well as the utilisation of higher pressure on the pressure side of the pump entail that the above-described dampers will attain far too short an operational running time. The air in the upright tubes is consumed rapidly and production stoppages become necessary.
There are also on the market a number of other types of dampers. Membrane dampers display a gas-filled space discrete from the product by the intermediary of a membrane. These dampers are expensive in operation, since the membrane often needs to be replaced. There are also specialist dampers which can be shut off and emptied of product, whereafter the air can once again be replenished. However, this entails not inconsiderable product losses.
Specialist inlet dampers provided with an external steam hat involve many parts which are difficult to clean and which may cause problems with regard to sterility in aseptic plants. Another type of damper is the resonator type which suffers from the drawback of being difficult to clean and thereby not suitable for food applications.